CN115589004A - Wind turbine generator frequency modulation method and system considering time delay characteristics - Google Patents
Wind turbine generator frequency modulation method and system considering time delay characteristics Download PDFInfo
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Abstract
The disclosure belongs to the technical field of wind power generation, and particularly relates to a wind turbine generator frequency modulation method and system considering time delay characteristics, wherein the method comprises the following steps: constructing a wind turbine generator system frequency response model considering the time delay characteristic; performing order reduction analysis on the constructed system frequency response model to obtain the lowest system frequency point of the wind turbine generator; based on the obtained lowest point of the system frequency, adopting droop control to calculate the frequency index of the wind turbine generator; and adjusting the droop coefficient in real time according to the obtained frequency index of the wind turbine generator, and finishing the wind turbine generator frequency modulation considering the time delay characteristic.
Description
Technical Field
The disclosure belongs to the technical field of wind power generation, and particularly relates to a wind turbine generator frequency modulation method and system considering time delay characteristics.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
With the implementation of the "double-carbon" environmental protection target, new energy power generation is receiving more and more attention. However, new energy power generation is connected to the grid through power electronic equipment, and the rotor speed and grid frequency decoupling characteristic prevents the system frequency change from being spontaneously responded to like a synchronous machine. With the background of increasing new energy permeability, the frequency safety of the power grid will be severely challenged.
In order to solve the problem of reduction of grid frequency safety caused by improvement of new energy permeability, domestic and foreign grid operation guide rules all stipulate that grid-connected operation wind turbine generators need to have the capacity of responding to grid frequency change, related documents propose various wind turbine generator participation grid frequency modulation strategies, and the wind turbine generator mainly has two modes of power standby and rotor kinetic energy utilization. Compared with a Power standby mode, the wind turbine generator can operate in a Maximum Power Point Tracking (MPPT) mode by utilizing the rotor kinetic energy mode, the economy is better, and therefore the frequency modulation mode utilizing the rotor kinetic energy needs to be researched.
At present, a wind turbine generator set utilizing rotor kinetic energy mainly comprises comprehensive inertia control, virtual synchronous machine control and variable phase-locked loop control in a power grid frequency control strategy. The comprehensive inertia control principle is clear, simple and feasible, and is a main research object in the text. The active reference value of the converter is changed through an additional power control link in the comprehensive inertia control, and the active reference value mainly comprises virtual inertia control and droop control; the virtual inertia control uses the frequency change rate as an input signal and aims to simulate the inertia response of the synchronous machine; droop control uses frequency deviation as an input signal and aims to simulate droop control of a synchronous machine.
Different from zero-delay inertia response of a synchronous machine, when the wind turbine generator adopts virtual inertia control to participate in power grid frequency modulation, the wind turbine generator is essentially quick in power response, and has inherent frequency measurement and communication links, and a certain delay exists in the process. In order to ensure the accuracy of frequency differential measurement, virtual inertia control generally needs 5-10 cycles of frequency measurement time, and communication delay is considered, and the inherent delay time can reach 300ms.
According to the knowledge of the inventor, the research on the virtual inertia delay characteristic is less at present, and the influence mechanism of the delay on the system frequency dynamic state is not clear, so that the virtual inertia delay characteristic needs to be subjected to modeling analysis. In addition, the virtual inertia has inherent defects of high requirement on frequency measurement precision, amplification measurement error of a frequency differential link and the like, and has poor reliability compared with droop control, and the virtual inertia generally has longer power response delay than the droop control due to the defects.
Disclosure of Invention
In order to solve the problems, the disclosure provides a wind turbine generator Frequency modulation method and System considering a delay characteristic, and researches feasibility of wind turbine generator Frequency modulation using droop control to replace virtual inertia control by analyzing and solving a System Frequency Response model (System Frequency Response, abbreviated as SFR) considering the delay characteristic of wind turbine generator virtual inertia control.
According to some embodiments, a first aspect of the present disclosure provides a wind turbine generator frequency modulation method considering a delay characteristic, which adopts the following technical scheme:
a wind turbine generator frequency modulation method considering time delay characteristics comprises the following steps:
constructing a wind turbine generator system frequency response model considering the time delay characteristic;
performing order reduction analysis on the constructed system frequency response model to obtain the lowest point of the system frequency of the wind turbine generator;
based on the obtained lowest point of the system frequency, adopting droop control to calculate the frequency index of the wind turbine generator;
and adjusting the droop coefficient in real time according to the obtained frequency index of the wind turbine generator, and finishing the wind turbine generator frequency modulation considering the time delay characteristic.
As a further technical limitation, when the system frequency deviates from a frequency reference value, comprehensive inertia control of the wind turbine generator participating in power grid frequency modulation is carried out by improving a control strategy of a converter, a frequency change rate and a frequency deviation signal are introduced into an active control link of the converter, additional power is added to a power instruction of the wind turbine generator, the magnitude of the additional power is in direct proportion to the frequency change rate and the frequency deviation, a comprehensive inertia control structure is obtained, wherein a part in the additional power, which is in direct proportion to the frequency change rate, is virtual inertia control, a part in the additional power, which is in direct proportion to the frequency deviation, is droop control, and the comprehensive inertia control is the combination of the virtual inertia control and the droop control,
wherein, delta P is the comprehensive inertia control, k d As a virtual inertia control coefficient, k p For the droop control coefficient, Δ f is the system frequency deviation.
As a further technical limitation, in the wind turbine, a wind power frequency modulation link is considered, a power control link of the wind turbine is added, comprehensive inertia control is adopted during frequency modulation, the constructed wind turbine system frequency response model considering the time delay characteristic is obtained, and the transfer function G(s) of the system frequency response model is
Wherein M is the inertia time constant of the system; d is the damping coefficient of the system; r is the system primary frequency modulation difference adjustment coefficient; f H Acting proportion for a high-pressure cylinder of a steam turbine of the system; t is R Is the reheat time constant of the system; alpha is the wind power permeability level;
system disturbance Δ P L In step form, the system frequency response expression delta f Z (s) is
Further, a Laus approximation method (Route approximation method) is adopted to reduce the order of the constructed system frequency response model, and a model transfer function R(s) after the order reduction is obtained is as follows:
wherein,
system of reduced order modelsThe frequency response is expressed as
After inverse laplace transform is performed on the system frequency response expression of the reduced order model, the time domain form delta f (t) of the system frequency response expression is obtained as follows:
wherein,
and (4) making the differential of the time domain form of the system frequency response expression equal to zero, and obtaining the time for reaching the lowest point of the frequency, namely obtaining the lowest point of the system frequency of the wind turbine generator system.
As a further technical limitation, the system frequency lowest point of the wind turbine is related to the wind permeability level, the system disturbance magnitude, the droop control coefficient of the wind turbine and the delay time of the wind turbine.
As a further technical limitation, when a system is disturbed, the lowest point of the system frequency is the point with the maximum influence degree after the system frequency is disturbed; and solving the wind turbine generator frequency index of the lowest point of the system frequency when the wind turbine generator participates in the frequency modulation of the power grid by adopting droop control analysis, wherein the wind turbine generator frequency index comprises the maximum frequency change rate and the steady-state frequency.
As a further technical limitation, the setting of the droop control coefficient is performed based on the same minimum frequency point and maximum frequency variation amount as those using the comprehensive inertia control; the droop coefficient of the wind turbine generator is adjusted in real time in the process of using the droop control to participate in the power grid frequency modulation, so that the wind turbine generator frequency modulation considering the time delay characteristic is completed.
According to some embodiments, a second aspect of the present disclosure provides a wind turbine generator frequency modulation system considering a time delay characteristic, which adopts the following technical scheme:
a wind turbine generator frequency modulation system considering time delay characteristics comprises:
a modeling module configured to construct a wind turbine system frequency response model that takes into account latency characteristics;
the analysis module is configured to perform order reduction analysis on the constructed system frequency response model to obtain a system frequency lowest point of the wind turbine generator;
a calculation module configured to calculate a wind turbine generator frequency index using droop control based on the obtained system frequency lowest point;
and the frequency modulation module is configured to adjust the droop coefficient in real time according to the obtained frequency index of the wind turbine generator, and complete the frequency modulation of the wind turbine generator considering the time delay characteristic.
According to some embodiments, a third aspect of the present disclosure provides a computer-readable storage medium, which adopts the following technical solutions:
a computer-readable storage medium, on which a program is stored, which program, when being executed by a processor, realizes the steps in the wind turbine frequency modulation method considering time delay characteristics according to the first aspect of the present disclosure.
According to some embodiments, a fourth aspect of the present disclosure provides an electronic device, which adopts the following technical solutions:
an electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor, where the processor executes the program to implement the steps in the wind turbine frequency modulation method considering the delay characteristic according to the first aspect of the disclosure.
Compared with the prior art, the beneficial effect of this disclosure is:
on the basis of analyzing and modeling the virtual inertia delay characteristic, analyzing and solving the lowest point of the system frequency through a model order reduction method, and providing a droop control coefficient setting method with the same frequency modulation effect as the comprehensive inertia control under the index of the lowest point of the frequency; when the time delay characteristic is considered, the virtual inertia does not have the capacity of sharing the disturbance power at the initial disturbance moment, is essentially quick power response and is consistent with droop control; meanwhile, the delay has no influence on the maximum frequency change rate and the steady-state frequency of the system, and the lowest point of the system frequency is reduced along with the increase of the delay; the droop control coefficient setting method based on the lowest frequency point index can be applied to different scenes; meanwhile, based on the droop control coefficient setting method in the text, the wind turbine generator can achieve the purpose of replacing virtual inertia control when only droop control is used, and can obtain better frequency modulation effect than when comprehensive inertia control is used.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.
Fig. 1 is a flowchart of a wind turbine frequency modulation method considering a delay characteristic in a first embodiment of the present disclosure;
FIG. 2 is a schematic diagram of an integrated inertial control architecture in accordance with a first embodiment of the disclosure;
FIG. 3 is a schematic structural diagram of an extended SFR model in which a wind turbine generator participates in power grid frequency modulation in the first embodiment of the disclosure;
fig. 4 is a schematic diagram illustrating an effect of virtual inertia delay on a maximum frequency drop of a system according to a first embodiment of the disclosure;
FIG. 5 is a schematic view of an alternative structure of a frequency modulation parameter of a wind turbine generator according to a first embodiment of the disclosure;
fig. 6 is a schematic diagram of droop control coefficient setting in the first embodiment of the present disclosure;
FIG. 7 is a diagram of a simulation structure of a two-region system in accordance with a first embodiment of the present disclosure;
fig. 8 (a) is a schematic diagram of system frequency deviation in a first embodiment of the present disclosure;
fig. 8 (b) is a schematic diagram of a frequency change rate of a system in accordance with a first embodiment of the present disclosure;
FIG. 9 (a) is a schematic diagram of a fan power increment and a virtual inertia response power under different delay conditions in the first embodiment of the disclosure;
FIG. 9 (b) is a diagram of the fan power increment and droop control response power under different delay conditions in the first embodiment of the present disclosure;
fig. 10 (a) is a schematic diagram of system frequency deviation and system frequency dynamics under different delay conditions in a first embodiment of the disclosure;
FIG. 10 (b) is a schematic diagram of system frequency deviation and initial system frequency dynamics of disturbance under different delay conditions according to a first embodiment of the disclosure;
FIG. 11 is a diagram illustrating an accuracy analysis of a model order reduction method for delay time variation according to a first embodiment of the disclosure;
fig. 12 is a schematic diagram of an accuracy analysis of a model order reduction method when frequency modulation parameters of a fan are different in a first embodiment of the disclosure;
fig. 13 (a) is a schematic diagram of a single droop control coefficient when the wind power permeability is 30% according to the first embodiment of the present disclosure;
fig. 13 (b) is a schematic diagram of a single droop control coefficient when the wind power permeability is 50% in the first embodiment of the present disclosure;
fig. 14 (a) is a schematic diagram illustrating comparison of system frequency deviations under different control modes in a first embodiment of the disclosure;
FIG. 14 (b) is a schematic diagram illustrating comparison of output energy of fans in different control modes according to the first embodiment of the present disclosure;
FIG. 14 (c) is a comparison diagram of the output power of the synchronous machine under different control modes in the first embodiment of the disclosure;
fig. 15 is a block diagram of a wind turbine generator frequency modulation system considering a delay characteristic in the second embodiment of the present disclosure.
Detailed Description
The present disclosure is further described with reference to the following drawings and examples.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
In the present disclosure, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only relational terms determined for convenience in describing structural relationships of the parts or elements of the present disclosure, and do not refer to any parts or elements of the present disclosure, and are not to be construed as limiting the present disclosure.
In the present disclosure, terms such as "fixedly connected," "connected," and the like should be understood broadly, and mean that they may be fixedly connected, integrally connected, or detachably connected; may be directly connected or indirectly connected through an intermediate. For persons skilled in the art, the specific meanings of the above terms in the present disclosure can be determined according to specific situations, and are not to be construed as limitations of the present disclosure.
The embodiments and features of the embodiments in the present disclosure may be combined with each other without conflict.
Example one
The first embodiment of the disclosure introduces a wind turbine generator frequency modulation method considering a time delay characteristic.
As shown in fig. 1, a wind turbine frequency modulation method considering a time delay characteristic includes:
constructing a wind turbine generator system frequency response model considering the time delay characteristic;
performing order reduction analysis on the constructed system frequency response model to obtain the lowest point of the system frequency of the wind turbine generator;
based on the obtained lowest point of the system frequency, adopting droop control to calculate the frequency index of the wind turbine generator;
and adjusting the droop coefficient in real time according to the obtained frequency index of the wind turbine generator, and finishing the wind turbine generator frequency modulation considering the time delay characteristic.
In the embodiment, an SFR model considering a delay link is established, aiming at the problem that a high-order model is difficult to analyze and solve a time domain analysis solution of the high-order model, order reduction of the high-order model and dynamic analysis and solution of system frequency are realized on the basis of a Route approximation method, the influence of delay on the dynamic state of the system frequency is analyzed on the basis of a key index analysis expression of the system frequency, and a theoretical basis is provided for substitutability analysis of virtual inertia.
When the wind turbine generator operates normally, the wind turbine generator works in the MPPT mode. When the system frequency f deviates from the frequency reference value f 0 And then, the wind turbine generator unit takes part in power grid frequency modulation by adopting comprehensive inertia control. The comprehensive inertia control is implemented by improving a converter control strategy, introducing a frequency change rate and a frequency deviation signal into an active control link of the converter, adding an additional power delta P on an original power instruction of a wind turbine generator, wherein the magnitude of the additional power is in direct proportion to the frequency change rate and the frequency deviation, and a control structure block diagram is shown in fig. 2; wherein, what is called virtual inertia control in proportion to the frequency change rate in the additional power, what is called droop control in proportion to the frequency deviation in the additional power, the comprehensive inertia control is the combination of the virtual inertia control and the droop control, and the expression is:
wherein, delta P is the comprehensive inertia control, k d As a virtual inertia control coefficient, k p For the droop control coefficient, Δ f is the system frequency deviation.
The wind turbine generator adopts comprehensive inertia control to participate in power grid frequency modulation, and is essentially quick in power response, and certain time delay exists. In practice, the virtual inertia generally has a longer frequency measurement time than the droop control in order to ensure the accuracy of the frequency differential measurement, and the power response delay is longer than that of the droop control.
In this embodiment, in order to simplify the analysis requirement, when the wind power frequency modulation uses the comprehensive inertia control, the virtual inertia control is consistent with the droop control power response delay, and the delay is approximately equivalent to a first-order inertia link, and the simplified wind turbine response power expression is as follows:
in the formula,. DELTA.P wind In order to consider the response power of the wind turbine generator during frequency modulation in the time delay characteristic, delta f (T) is the system frequency response during frequency modulation, T d And the equivalent time constant is the virtual inertia delay of the wind turbine generator. According to the formula (2), the wind turbine generator response power during frequency modulation is determined by the virtual inertia control coefficient, the frequency change rate signal, the droop control coefficient and the frequency deviation signal, and the power response time depends on the time delay. Therefore, the delay mainly affects the response time of the additional power of the wind turbine generator, and further affects the frequency dynamics of the system.
Further considering a wind power frequency modulation link, adding a power control link of the wind turbine generator on the basis of a classical SFR model, and establishing an extended SFR model considering the wind turbine generator power response delay, as shown in FIG. 3. The wind turbine generator adopts comprehensive inertia control during frequency modulation, and simultaneously considers the wind turbine permeability level and the wind turbine generator power response delay.
In FIG. 3, M is the inertial time constant of the system; d is the damping coefficient of the system; r is a system primary frequency modulation difference adjustment coefficient; f H Acting proportion for a high-pressure cylinder of a steam turbine of the system; t is a unit of R Is the reheat time constant of the system; alpha is the wind power permeability level; namely, the system transfer function G(s) obtained based on the extended SFR model is as follows:
after simplification, the method can be obtained:
wherein,
consider that disturbances in the form of steps in the power system are most common and most influential, such as generator tripping, sudden load increases, etc. Suppose system disturbance Δ P L In a step-wise fashion. When disturbance occurs, the system frequency response expression Δ f Z (s) is:
the formula (4) and the formula (5) can obtain that the system frequency response model considering the virtual inertia delay has high-order characteristics, and the time domain analysis solution is difficult to directly solve. Therefore, the order reduction and time domain solution of the high-order model are carried out by using a Router approximation method.
Based on the formula (4), when the virtual inertia delay characteristic is considered, the system frequency response model is third order, and the transfer function characteristic equation is a third order parameter equation. The third-order parameter equation cannot be resolved, so that the system model cannot be resolved in a time domain, and further cannot obtain an analytical expression of system frequency dynamics. In this embodiment, a Routh approximation method is used to reduce the order of a system model, and a transfer function R(s) of the reduced-order model is obtained as follows:
in the formula,
from equation (5), the frequency response expression of the reduced order model system is:
the inverse laplace transform is performed on the formula (7) to obtain a time domain form Δ f (t) of a system frequency response expression, wherein the time domain form Δ f (t) is as follows:
in the formula,
the time of reaching the lowest point of the frequency can be obtained by making the system frequency response differential equal to zero, and the system frequency response differential is obtained:
when the trigonometric function term in the bracket on the right side of the formula (9) is zero, the system frequency response differential is zero, namely the time t reaching the lowest point of the frequency is obtained m Comprises the following steps:
in the formula (10), the k value is shown
And arctan (-delta/omega), if the sum of the two angles is in two or three quadrants, the k value is 1, otherwise 0. Substituting the formula (10) into the formula (8) to obtain the lowest point of the system frequency Δ f max The expression is as follows:
as can be seen from the formula (11), the conventional synchronous unit parameters M, D and T in the system R 、F H Wind power permeability level alpha and system disturbance size delta P L Known as the lowest point of the system frequency Δ f max Virtual inertia control coefficient k of wind turbine generator d Droop control coefficient k p And virtual inertia delay time T d And (6) determining.
Currently, the frequency response of a power system after active disturbance is evaluatedThe indexes of good and bad mainly include three maximum frequency drop delta f max Maximum rate of change of frequency df/dt and steady-state frequency Δ f set . The embodiment researches an influence mechanism of virtual inertia delay on system frequency dynamics based on a system frequency response index.
According to the solved system frequency minimum point analytical expression, as shown in formula (11), the system frequency maximum change rate and the steady state frequency drop can be respectively solved by the laplace transform initial value theorem and final value theorem, as shown in formula (12) and formula (13):
analyzing the formula (12), it can be seen that, when the delay characteristic is not considered, the virtual inertia can share the disturbance power at the initial moment of disturbance, so that the maximum change rate of the frequency is reduced along with the increase of the virtual inertia coefficient, and the effect of synchronous machine inertia support is realized. However, when the delay characteristic is considered, the virtual inertia does not have the capability of sharing the disturbance power at the initial moment of the disturbance, and the essence is a fast power response with delay, so that the maximum change rate of the system frequency is independent of the delay.
Analyzing the formula (13), it can be obtained that the steady-state frequency is only related to the disturbance magnitude, the synchronous machine difference adjustment coefficient, the wind power permeability level, the synchronous machine damping coefficient and the fan droop control coefficient, and is not related to the delay magnitude.
The influence of the time delay on the maximum frequency drop of the system can be obtained by analyzing the formula (11), and the formula (11) shows that the maximum frequency drop is obtained by the frequency modulation parameter k of the wind turbine under the condition that the conventional synchronous generator parameter and the wind power permeability of the system are determined d 、k p And virtual inertia power response delay T d And (6) determining.
Assigning typical values to variables irrelevant to the frequency modulation parameters of the wind turbine generator in the expression, namely, parameters M =10 of a synchronous machine, D =1; regulating deviceSpeed parameter: r =0.05,t R ＝10，F H =0.3; wind power permeability: α =0.3; disturbance: delta P L U. =0.1p.u. On the basis of the above, the analysis results in the conclusion that the lowest point of the system frequency is reduced along with the increase of the time delay, as shown in fig. 4.
Therefore, the virtual inertia power response delay has no influence on the maximum frequency change rate and the steady state frequency drop of the system, and the lowest point of the system frequency is reduced along with the increase of the delay. When the delay characteristic is considered, the virtual inertia control cannot share the disturbance power at the initial moment of disturbance, and is different from the inertia response of a synchronous machine, and the virtual inertia control is essentially quick power response with delay and is consistent with droop control. Meanwhile, the virtual inertia control has the inherent defects of high frequency measurement precision requirement, amplification measurement error in a frequency differentiation link and the like, and the reliability is poor compared with the droop control, and the defects cause that the virtual inertia generally has longer power response delay than the droop control. Therefore, in order to avoid the disadvantage of the virtual inertia, the embodiment performs related research on the feasibility of using droop control instead of virtual inertia control for the wind turbine generator.
And analyzing and solving to obtain a system frequency lowest point expression when the wind turbine generator only uses the droop control to participate in the power grid frequency modulation, providing a droop control coefficient setting method based on the system frequency lowest point index, focusing on the maximum frequency change rate and the steady-state frequency index, and analyzing the feasibility of using the droop control to replace the virtual inertia with the time delay.
And a frequency modulation mode of rotor kinetic energy is utilized, so that the wind turbine generator provides droop control based on the kinetic energy of the blade rotor. The virtual inertia generally has a longer frequency measurement time than that of droop control in order to ensure the accuracy of frequency differential measurement, so that when the virtual inertia and the droop control energy are both derived from the kinetic energy of the blades, the response delay of the droop control power is smaller than that of the virtual inertia control. From equation (2), the response power when the wind power frequency modulation only uses droop control is:
wherein, T' d Is the equivalent time constant of the droop control delay.
The system model of the wind turbine generator set only using droop control to participate in power grid frequency modulation can be obtained by replacing the transfer function of the wind turbine generator set power response feedback channel in the SFR model shown in FIG. 3 with a formula (14). Namely, the system model when the wind power frequency modulation only uses the droop control can be obtained by using the system model when the wind power frequency modulation uses the comprehensive inertia control through the displacement relation shown in the formula (15):
similarly, the system transfer function G '(s) and the system frequency response expression Δ f'(s) when the wind power frequency modulation uses droop control are as follows:
wherein, each variable is obtained by only using the displacement relation shown in the formula (15) for each variable in the formula (4). According to the formula (16), the system frequency response model is three-order when the wind turbine generator only uses droop control to participate in power grid frequency modulation, so that the system transfer function still needs to be reduced based on a Routh approximation method when the system frequency response expression is solved, and the reduced model transfer function R'(s) is as follows:
wherein, each variable is obtained by only using the displacement relation shown in the formula (15) for each variable in the formula (6). According to the formula (7), the formula (8), the formula (9), the formula (10) and the formula (11), when the wind turbine generator only uses the droop control to participate in the frequency modulation of the power grid, the system frequency minimum point solutionAnalytic expression delta f' max Comprises the following steps:
wherein, each variable is obtained by replacing each variable in the formula (8) through the formula (15). From the formula (19), the conventional synchronous unit parameters M, D, T in the system R 、F H Wind power permeability level alpha and system disturbance size delta P L Known case, lowest point of system frequency Δ f' max Droop control coefficient k 'of wind turbine generator unit' p And a delay time of T' d And (6) determining. Droop coefficient setting method based on frequency lowest point equivalence
After active disturbance occurs, the lowest point of the system frequency represents the condition that the system frequency is influenced to the maximum extent after the disturbance, and the lowest point is an important index for evaluating the safety of the system frequency. Therefore, in the embodiment, the lowest point of the system frequency is used as an index, and the droop control coefficient setting method is researched when the lowest point of the system frequency is equal to that when the wind turbine generator only uses the droop control and uses the comprehensive inertia control. When the lowest points of the system frequencies of the two control modes used by the wind turbine generator are equal, the following relations are satisfied:
Δf′ max (k′ p )＝Δf max (k d ,k p ) (20)
wherein, delta f' max (k′ p ) The lowest point of the system frequency for a wind turbine using only droop control, i.e. equation (19), Δ f max (k d ,k p ) And (3) using the lowest point of the system frequency when the comprehensive inertia control is used for the wind turbine generator, namely the formula (11).
As can be obtained from the formula (20), the frequency modulation parameter substitution relationship between the two control modes is:
k′ p ＝g(k d ,k p ) (21)
the structure diagram of the alternative relationship between the frequency modulation parameters of the two control modes is shown in fig. 5.
According to the formula (20), the conventional synchronous unit parameters and wind power penetration of the systemUnder the condition that the frequency level, the system disturbance magnitude and the wind turbine power response delay are known, the lowest point of the system frequency is only the frequency modulation parameter k of the wind turbine d 、k p And (6) determining. Therefore, the lowest point expression of the system frequency is compared with the frequency modulation parameter k of the wind turbine generator d 、k p Irrelevant variables are assigned typical values. Meanwhile, the power response delay of the wind power frequency modulation using comprehensive inertia control is taken as T d =500ms, power response delay is taken as T 'using droop control only' d =400ms. The value range of the frequency modulation control parameter of the wind turbine generator is set as follows: k is a radical of formula d ∈[8,12]，k p ∈[15,25](ii) a The coefficient setting when solving the available wind power frequency modulation and only using droop control is shown in fig. 6; in fig. 6, the x and y axes respectively represent the virtual inertia coefficient k when the wind power frequency modulation uses the comprehensive inertia control d And droop control coefficient k p And z-axis represents coefficient k 'when wind power frequency modulation is only used for droop control' p 。
Alternative feasibility analysis based on frequency dynamic key indexes
The embodiment focuses on the dynamic key indexes (the lowest frequency point, the steady-state frequency and the maximum frequency reduction rate) of the system frequency, and the feasibility of using droop control to replace virtual inertia control by the wind turbine generator is analyzed. The droop control coefficient setting method in the embodiment is obtained by making the lowest point of the system frequency equal when the wind power frequency modulation is only controlled by using droop and when the comprehensive inertia control is used.
Solving the maximum frequency change rate and the steady-state frequency deviation when the wind power frequency modulation only uses the droop control, as shown in the formula (22) and the formula (23):
comparing the formula (12) with the formula (22), the maximum frequency change rate of the system is irrelevant to the frequency modulation control parameters of the wind turbine generator, so that the wind power frequency modulation only enables the wind power frequency modulationThe maximum frequency change rate of the system is the same when the droop control is used as the comprehensive inertia control. Comparing the formula (13) with the formula (23), the system steady-state frequency deviation and the droop control coefficient k of the wind turbine generator can be obtained p Is in negative correlation, k p The larger the steady state frequency deviation, the smaller the steady state frequency deviation, and the higher the steady state frequency. As can be seen from the formula (21) and fig. 6, when the wind power frequency modulation only uses the droop control, the droop control coefficient needs to be increased appropriately in order to obtain the same lowest frequency point as that when the comprehensive inertia control is used, so that when the wind power frequency modulation only uses the droop control, the steady-state frequency is increased compared with that when the comprehensive inertia control is used.
The droop control coefficient setting method based on the system frequency lowest point index can not only obtain the same frequency lowest point and the maximum frequency change rate as those obtained when the comprehensive inertia control is used, but also improve the system steady-state frequency. When the wind turbine generator only uses droop control to participate in power grid frequency modulation, the purpose of replacing virtual inertia control can be achieved by properly increasing droop control coefficients, and a better frequency modulation effect can be achieved compared with the effect of using comprehensive inertia control.
In order to verify the correctness of the influence mechanism of the wind turbine generator power response delay on the system frequency control and the feasibility of the droop control coefficient setting method, which are analyzed by the embodiment, a two-region system simulation model including a thermal power generating unit and a wind turbine generator is built on the basis of a simulation platform, a simulation structure chart is shown in fig. 7, and the operation parameters of the thermal power generating unit and a wind power plant are shown in tables 1 and 2.
TABLE 1 thermal power generating unit simulation parameters
TABLE 2 simulation parameters of wind turbine
The virtual inertia differential link is easy to amplify the measurement error, and the delay characteristic of the virtual inertia differential link has adverse effect on the response power of the fanSounding; the specific setup simulation is as follows: setting the initial wind speed of a wind power plant to be 15m/s, the output of the wind power plant to be 30MW, the initial active load of a system to be 103MW, and the frequency modulation parameter k of the wind turbine generator d ＝10,k p =20, assuming a load surge event of 6MW occurs at 40s in the system, the system frequency dynamics and its differential signal simulation curve are shown in fig. 6; then, the influence of the delay characteristic on the virtual inertia and the droop control response power is analyzed under the three conditions that the virtual inertia delay size is 0.2s, 0.5s and 1.0s respectively, and simulation curves are shown in fig. 8 (a) and fig. 8 (b).
Because the virtual inertia control output power of the wind turbine generator is in direct proportion to the system frequency differential, the differential link has the problems of high measurement precision requirement, amplification measurement error and the like, and the influence is particularly serious when the system frequency oscillates. Fig. 8 (a) shows a dynamic curve of the system frequency after the disturbance occurs, and fig. 8 (b) shows a signal curve of the rate of change of the system frequency at the initial moment of the disturbance. It can be seen that there are many fluctuating signals in the system frequency differential signal, and the amplification measurement error has obvious effect.
The virtual inertia control aims at simulating instantaneous inertia response of the synchronous machine, and shares disturbance power at the initial moment of disturbance to enable the output power to change suddenly. However, it is essentially a power response with a delay, which cannot provide instantaneous power support at the initial moment of disturbance due to the presence of the delay, while the magnitude of the virtual inertia control response power decreases with the increase of the delay, as shown in fig. 9 (a). The droop control is designed to simulate the primary frequency modulation of a synchronous machine, the response power of the droop control is proportional to the frequency deviation, strong support can be provided near the lowest point of the system frequency, and the droop control can provide strong support near the lowest point of the system frequency regardless of the delay, as shown in fig. 9 (b).
In order to verify the influence mechanism of the virtual inertia delay characteristic on the system frequency dynamics, the simulation is set as follows: the simulation parameters are consistent with section 3.1.1, and the influence of the virtual inertia delay on the system frequency response is analyzed under the three conditions that the virtual inertia delay is 0.2s, 0.5s and 1.0s respectively, and the simulation curves are shown in fig. 10 (a) and 10 (b).
When a sudden load increase event occurs in the system, the wind turbine generator provides additional power to respond to the frequency change of the power grid through virtual inertia and droop control. However, this process is a power response with a certain time delay, and the time delay mainly affects the time of the wind turbine generator additional power response during the frequency modulation, so that the lowest point of the frequency is reduced along with the increase of the time delay, as shown in fig. 10 (a). The maximum frequency change rate of the system occurs at the initial disturbance moment, and due to the existence of the delay, the virtual inertia control of the wind turbine generator cannot share the disturbance power at the initial disturbance moment to cause the output power to change suddenly, so that the maximum frequency change rate of the system is irrelevant to the delay, as shown in fig. 10 (b). Meanwhile, as can be seen from fig. 10 (a), the steady-state frequency of the system is also independent of the delay size.
Therefore, the virtual inertia delay has adverse effects on the system frequency dynamics, the system frequency minimum point is mainly affected by the virtual inertia delay, and the larger the delay is, the lower the system frequency minimum point is, so that mechanism model construction and quantitative analysis are required.
Effectiveness verification based on route approximation order reduction
And verifying the effectiveness of the system frequency lowest point analytic expression obtained by the model order reducing method by comparing the system frequency lowest point analytic expression obtained by the model order reducing method with a result obtained by SFR model time domain simulation.
Firstly, the accuracy of the model order reduction method is verified when the delay time is different, and under the condition that the fan power response delay time is different, the point pair of the system frequency lowest point obtained by analyzing and solving through the model order reduction method and the frequency lowest point obtained by the SFR model time domain simulation method is shown in fig. 11. Therefore, the results obtained by the two methods are very similar, the maximum error is not more than 0.035Hz, and the error is not more than 10%, so that the analytic expression of the lowest point of the system frequency obtained by the model order reduction method is effective.
The accuracy of the model order reduction method in the process of researching the frequency modulation parameters of different wind turbine generators is characterized in that the value range of the frequency modulation control parameters of the wind turbine is set as follows: k is a radical of d ∈[8,12]，k p ∈[15,25]And the power response delay of the wind turbine generator is T d =500ms. Under different wind turbine generator frequency modulation parameters, the system frequency lowest point obtained by analyzing and solving through a model order reduction method and the SFR model time domain simulation methodThe resulting frequency nadir error is shown in fig. 12. Therefore, the results obtained by the two methods are very similar, the maximum error is not more than 0.055Hz, and the error is not more than 15%, so that the analytic expression of the lowest point of the system frequency obtained by the model order reduction method is effective.
When the system model has high-order characteristics and is difficult to analyze and solve, the order of the high-order system model is reduced by a model order reduction method, and then the analysis and solution of the reduced-order model are effective.
In order to verify the applicability of the droop control parameter setting method provided in the embodiment in different scenes, the simulation model parameters shown in tables 1 and 2 are used, and the frequency modulation parameters of the wind turbine generator set only using droop control are solved under different wind power permeabilities. The output of the wind turbine is set to 30MW and 45MW respectively, and the setting method of the droop control coefficient is shown in fig. 13 (a) and 13 (b).
As can be seen from fig. 13 (a) and 13 (b), the droop control coefficient setting method based on the lowest point index of the system frequency is applicable to different wind power permeability scenarios. Comparing fig. 13 (a) and fig. 13 (b) at the same time, as the wind power permeability increases, since the inertia level of the system decreases, when the same load disturbance occurs, the system drop speed increases, and more droop control coefficients need to be added to obtain the same system frequency lowest point as the comprehensive inertia control.
Therefore, under different wind turbine generator operation scenes, the droop control coefficient which is the same as the lowest frequency point when the wind turbine generator uses comprehensive inertia control can be obtained based on the droop control coefficient setting method provided by the embodiment. Substitutable simulation verification with delayed virtual inertia
In order to verify the feasibility of using droop control instead of virtual inertia control in the wind turbine generator set in the embodiment, the simulation is set as follows: assuming that the frequency modulation parameter is k when the wind turbine generator participates in the frequency modulation of the power grid by comprehensive inertia control d ＝10,k p =20, and the other parameters are consistent with the section 3.1.1 simulation parameters, and the frequency modulation parameter k 'when the wind turbine generator uses droop control is obtained' p =24.49. Simulation of wind power frequency modulation when only droop control and comprehensive inertia control are usedThe curves are shown in fig. 14 (a), 14 (b), 14 (c) and table 3.
TABLE 3 comparison of system frequency response indexes under different wind turbine control modes
As shown in fig. 14 (a) and table 3, according to the droop control coefficient setting method given in the present embodiment, the wind turbine generator can obtain the same lowest frequency point when the droop control is used as when the comprehensive inertia control is used. Meanwhile, the steady-state frequency deviation of the system is in negative correlation with the droop control coefficient, and the droop control coefficient is increased compared with the droop control method using comprehensive inertia control because the wind power frequency modulation only uses the droop control. Therefore, the steady-state frequency deviation of the system is reduced, and the steady-state frequency is improved.
When the wind power frequency modulation uses the comprehensive inertia control, the power support is provided through the virtual inertia control and the droop control, and when the wind power frequency modulation only uses the droop control, the wind turbine generator only provides the power support through the droop control. In the initial stage of disturbance, the system frequency change rate is large, the system frequency deviation is small, and as the output power of the virtual inertia control is in direct proportion to the system frequency change rate and the output power of the droop control is in direct proportion to the system frequency deviation, the comprehensive inertia control can provide stronger power support compared with the droop control. And near the lowest point of the system frequency, the change rate of the system frequency is small, the deviation of the system frequency is large, and because the droop control coefficient is increased when the wind turbine generator only uses the droop control compared with the droop control when the comprehensive inertia control is used, stronger power support can be provided, as shown in fig. 14 (b) and 14 (c).
Based on the droop control coefficient setting method in the embodiment, the purpose of replacing virtual inertia control can be achieved when only droop control is used by the wind turbine generator, and a better frequency modulation effect can be obtained compared with the frequency modulation effect when comprehensive inertia control is used.
According to the method, analysis and alternative research of an influence mechanism model of the virtual inertia delay of the wind turbine generator are carried out; firstly, approximately equating the time delay characteristics of the virtual inertia and the droop control of the wind turbine generator as a first-order inertia link, and establishing a system frequency response model of the virtual inertia and the droop control used for wind power frequency modulation; secondly, performing order reduction analysis on the high-order model based on a Laus approximation method to obtain an analysis expression of the lowest point of the system frequency; then, an SFR model of wind power frequency modulation only using droop control is solved through analysis, and a droop control coefficient setting method with the same frequency modulation effect as virtual inertia and droop control is given under the index of the lowest frequency point; under the condition of setting droop control parameters, comparing key index relations of maximum frequency change rate, steady-state frequency and the like under two control modes to obtain a properly changed droop coefficient, so that the purpose of replacing virtual inertia with time delay can be realized, and a conclusion that the frequency modulation effect is better than that of virtual inertia and droop control can be obtained; and finally, establishing a simulation model, and verifying the correctness of analysis from the response power of the wind turbine generator, the frequency modulation energy demand, the system frequency response dynamic state and the like.
Example two
The second embodiment of the disclosure introduces a wind turbine generator frequency modulation system considering the time delay characteristic.
Fig. 15 shows a wind turbine generator frequency modulation system considering delay characteristics, which includes:
a modeling module configured to construct a wind turbine system frequency response model that takes into account latency characteristics;
the analysis module is configured to perform order reduction analysis on the constructed system frequency response model to obtain a system frequency lowest point of the wind turbine generator;
a calculation module configured to calculate a wind turbine generator frequency index using droop control based on the obtained system frequency lowest point;
and the frequency modulation module is configured to adjust the droop coefficient in real time according to the obtained wind turbine generator frequency index, and complete wind turbine generator frequency modulation considering the time delay characteristic.
The detailed steps are the same as those of the wind turbine generator frequency modulation method considering the time delay characteristic provided in the first embodiment, and are not described herein again.
EXAMPLE III
The third embodiment of the disclosure provides a computer-readable storage medium.
A computer-readable storage medium, on which a program is stored, which, when executed by a processor, implements the steps in the wind turbine frequency modulation method considering the delay characteristics according to the first embodiment of the disclosure.
The detailed steps are the same as those of the wind turbine generator frequency modulation method considering the time delay characteristic provided in the first embodiment, and are not described herein again.
Example four
The fourth embodiment of the disclosure provides an electronic device.
An electronic device includes a memory, a processor, and a program stored in the memory and executable on the processor, where the processor executes the program to implement the steps in the wind turbine frequency modulation method considering the delay characteristics according to the first embodiment of the disclosure.
The detailed steps are the same as those of the wind turbine generator frequency modulation method considering the time delay characteristic provided in the first embodiment, and are not described herein again.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.
Claims (10)
1. A wind turbine generator frequency modulation method considering time delay characteristics is characterized by comprising the following steps:
constructing a wind turbine generator system frequency response model considering the time delay characteristic;
performing order reduction analysis on the constructed system frequency response model to obtain the lowest point of the system frequency of the wind turbine generator;
based on the obtained lowest point of the system frequency, adopting droop control to calculate the frequency index of the wind turbine generator;
and adjusting the droop coefficient in real time according to the obtained frequency index of the wind turbine generator, and finishing the wind turbine generator frequency modulation considering the time delay characteristic.
2. The method as claimed in claim 1, wherein when the system frequency deviates from the frequency reference value, the comprehensive inertial control of the wind turbine generator participating in the grid frequency modulation is performed by improving the control strategy of the converter, the frequency variation rate and the frequency deviation signal are introduced into the active control link of the converter, the additional power is added to the power command of the wind turbine generator, the magnitude of the additional power is proportional to the frequency variation rate and the frequency deviation, so as to obtain the comprehensive inertial control structure, wherein the portion of the additional power proportional to the frequency variation rate is the virtual inertial control, the portion of the additional power proportional to the frequency deviation is the droop control, so as to obtain the comprehensive inertial control which is the combination of the virtual inertial control and the droop control,
wherein, delta P is the comprehensive inertia control, k d As a virtual inertia control coefficient, k p For the droop control coefficient, Δ f is the system frequency deviation.
3. The method for modulating frequency of a wind turbine generator with consideration of time delay characteristics as claimed in claim 1, wherein in the wind turbine generator, a wind turbine frequency modulation link is taken into consideration, a power control link of the wind turbine generator is added, and comprehensive inertia control is adopted during frequency modulation to obtain the constructed wind turbine generator system frequency response model with consideration of time delay characteristics, wherein a transfer function G(s) of the system frequency response model is
Wherein M is the inertia time constant of the system; d is the damping coefficient of the system; r is a system primary frequency modulation difference adjustment coefficient; f H Acting proportion for a high-pressure cylinder of a steam turbine of the system; t is R Is the reheat time constant of the system; alpha is the wind power permeability level;
system disturbance Δ P L In step form, the system frequency response expression delta f Z (s) is
4. The wind turbine generator frequency modulation method considering the delay characteristic as set forth in claim 3, wherein a Laus approximation method is adopted to reduce the constructed system frequency response model, and the model transfer function R(s) after reduction is obtained is:
wherein,
the frequency response of the system of the reduced order model is expressed as
After inverse laplace transform is performed on the system frequency response expression of the reduced order model, the time domain form delta f (t) of the system frequency response expression is obtained as follows:
wherein,
and (4) making the differential of the time domain form of the system frequency response expression equal to zero, and obtaining the time for reaching the lowest point of the frequency, namely obtaining the lowest point of the system frequency of the wind turbine generator system.
5. A method of frequency modulation of a wind turbine in consideration of time delay characteristics as claimed in claim 1 wherein the system frequency minimum of said wind turbine is related to wind permeability level, system disturbance magnitude, droop control coefficient of the wind turbine and delay time of the wind turbine.
6. The wind turbine generator frequency modulation method considering the time delay characteristics as claimed in claim 1, wherein when the system is disturbed, the lowest point of the system frequency is a point at which the system frequency is influenced to the maximum extent after being disturbed; and solving the wind turbine generator frequency index of the lowest point of the system frequency when the wind turbine generator participates in the frequency modulation of the power grid by adopting droop control analysis, wherein the wind turbine generator frequency index comprises the maximum frequency change rate and the steady-state frequency.
7. A wind turbine frequency modulation method considering delay characteristics as claimed in claim 1, wherein the setting of the droop control coefficient is performed based on the same frequency lowest point and maximum frequency variation amount as those using the synthetic inertia control; the droop coefficient of the wind turbine generator is adjusted in real time in the process of using the droop control to participate in the power grid frequency modulation, so that the wind turbine generator frequency modulation considering the time delay characteristic is completed.
8. The utility model provides a wind turbine generator system frequency modulation system of considering time delay characteristic which characterized in that includes:
a modeling module configured to construct a wind turbine system frequency response model that takes into account latency characteristics;
the analysis module is configured to perform order reduction analysis on the constructed system frequency response model to obtain the lowest point of the system frequency of the wind turbine generator;
a calculation module configured to calculate a wind turbine generator frequency index using droop control based on the obtained system frequency lowest point;
and the frequency modulation module is configured to adjust the droop coefficient in real time according to the obtained wind turbine generator frequency index, and complete wind turbine generator frequency modulation considering the time delay characteristic.
9. A computer-readable storage medium, on which a program is stored, which program, when being executed by a processor, carries out the steps of the method for frequency modulation of a wind turbine generator taking into account a time-delay characteristic as claimed in any one of claims 1 to 7.
10. An electronic device comprising a memory, a processor and a program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method for frequency modulation of a wind turbine generator considering delay characteristics as claimed in any one of claims 1 to 7.
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